Photo-electret multiple copy process



Jan 16, 1968 R. A. FEHLBERG ETAL 3,364,020

PHOTO-ELECTRET MULTIPLE COPY PROCESS Filed April 1, 1964 7e 2 f z j 75 yfm2 40 3@ 35 l FGIS 3 D CK FIG- 4 INVENTS ,QcharcZA Fell/bezig UnitedStates Patent O 3 364 020 rnoroarnornnr MULETIPLE -corv rnocnss RichardA. Feldberg, Mundelein, and Dave R. Kazen, Niles, Ill., assignors to A.B. Dick Company, Niles, Ill., a corporation of Illinois Filed Apr. 1,1964, Ser. No. 356,389 Claims. (Cl. 96-1) ABSTRACT 0F THE DISCLOSURE Anelectrostatic copy process for producing more than one copy from animaged electret in the form of a phosphor which includes positioning theelectret layer between electrodes and passing a D-C potentialof 50-500volts between the electrodes and simultaneously exposing the electretlayer to radiations either in the form of an overall pattern to polarizethe phosphor layer or in the form of a light pattern corresponding tothe image to effect internal polarization of the exposed portions. Inthe event that the phosphor layer is formed with overall internalpolarization, it is exposed to a light pattern in the absence of theexternal electrical field to dissipate the internal polarization fromthe exposed portions. The electret layer having the latent polarizedimage is developed with a toner, a copy sheet is positioned in surfacecontact with the toned side of the electret and the assembly ispositioned between electrodes for the passage of a potentialtherebetween for effecting transfer of the toner from the electret tothe adjacent surface of the copy sheet without destroying the internallypolarized image in the electret layer. The copy sheet is separated fromthe electret and the image is set thereon while the steps from thedevelopment of the internally polarized image are repeated any number oftimes for the production of additional copy without the need forresensitization or exposure of the electret layer.

This invention relates to a copy process and it relates moreparticularly to an electrostatic dry copy process from which more thanone copy can be produced from a single exposure.

In the electrostatic copy process developed by Dr. Carlson, U.S. PatentNo. 2,297,691, a photo-conductive layer on an electrically conductivebase is charged in an overall pattern by corona discharge from anelectrostatic source. Thereafter the charge is destroyed from portionsexposed to light through an original to leave a latent electrostaticimage which can be developed by a suitable pigment powder or toner.' Thetoner can be set on the dielectric coating to produce a single copy orthe toner on the developed image can be transferred to a copy sheetbrought into surface contact with the developed image by reversal of theelectrostatic charge. In either event, the latent electrostatic image isdestroyed upon the development of the copy with the result that only onecopy can be secured per exposure.

Formation of the charge by corona discharge in the process of Dr.Carlson represents a surface phenomenon wherein it is diilicult toretain the latent electrostatic image on the surface over an extendedperiod of time. More recently, a technique has been developing wherein alatent electrostatic image is formed in depth through a phosphor layer,hereinafter referred to as an electret, whereby a more stableelectrostatic image is formed in the electret to offer the possibilitiesof image retention .for a time sufcient to produce one or more copiesfrom a single eX- posure.

In an article entitled, Data Storage and Display with PolarizedPhosphors, by H. P. Kallmann and J. Rennert, Electronics, Aug. 28, 1959(pages 39-41), description is 3,364,020 Patented Jan. 16, 1968 ICC madeof a photo-electret in which the latent electrostatic image is formed byexposure of the phosphor simultaneously to a D-C field and to radiationsto cause internal polarization of the phosphor. In the arrangementdescribed in the aforementioned article, the phosphor is imaged byselective radiation, in the dark, of portions of the phosphor to beimaged while an overall D-C field on the order of 50-500 volts isapplied. This causes internal polarization in the portions radiated toproduce a latent electrostatic image. The image is retained over anextended period of time if the phosphor is confined to the dark. Theimage can be wiped out by exposure to radiations such as light,infrared, ultra violet and the like. Instead of exposing the phosphorsimultaneously to the D-C field and the selective radiations, an overallpolarization can be effected by simultaneous exposure of the electret tothe D-C eld and to light in an overall pattern after which exposure ofthe charged electret to light through a transparent original or the likewill effect removal of the charge in the nonimaged portions, leaving theelectret with the latent electrostatic image for subsequent development.

It has been suggested that, by reason of the volumetric characteristicof the latent electrostatic image developed in the electret, as comparedto the surface charge characteristic of the process of Dr. Carlson, thelatent electrostatic image might be capable of being retained in theelectret for a time sufficient to develop more than one copy perexposure. However, the systems that have been suggested tend to destroythe latent electrostatic image during development or transfer with theresult that the imaged electret is suitable only for the production ofbut one good copy per each exposure.

It is an object of this invention to provide a method and means wherebyan electret having a latent electrostatic image formed therein can beused to produce one or multiple copies of good quality from a singleexposure and it is a related object to provide a method and means of thetype described which is simple in construction and easy in operation,which does not require additional expense or complicated equipment, andwhich is capable of reduction to a commercially desirable copy processfor the production of multiple copies from a single' exposure.

These and other objects and advantages of this invention willhereinafter appear and for` purposes of illustration, but not oflimitation, an embodiment of the invention is shown in the accompanyingdrawing, in which:

FIG. l is a schematic sectional elevation view of the arrangement ofelements for use in the production of a charged electret in accordancewith the teachings of the aforementioned article of Kallmann et al.;

FIG. 2 is a perspective view of the developed latent electrostatic imageon the electret;

FIG. 3 is a schematic sectional elevational view of the arrangement ofelements for transfer of the developed image from the imaged electret toa copy sheet in accordance with the practice of this invention; and

FIG. 4 is a top plan view of the copy that is produced.

The concept of this invention resides in the processing of the electret,independent of the manner in which the latent electrostatic image isfor-med, to produce one or more copies of good quality from the imagedelectret Without destruction of the latent electrostatic image. Theinvention is applicable to a photo-electret imaged as by the processdescribed in the aforementioned article of Kallmann et al., or by otherprocesses heretofore or hereafter developed for producing a latentelectrostatic image by polarization or by volumetric orientation ofcharges in a phosphor coating.

For purposes of illustration, brief description will hereinafter be madeof the process for preparing an imaged electret in accordance with theteachings of Kallmann et al.

Example 1.--Preparatin of charged electret Referring to FIG. 1 of thedrawing, a phosphor layer of zinc cadmium sulfide doped with about 0.5%by weight of silver and bonded with an organo silicon resin is providedon a paper base sheet 12 to form an electret 14. A voltage of 50 voltsD-C is applied to external electrodes 15 and 18 positioned on oppositesides of the electret 14 for l0 seconds. During this period, thephosphor layer is excited by a 2 microseeond light ash from an xenon ashtube 2t) through a transparent original 22 to impress a polarized lightsignal into the electret which functions as the latent electrostaticimage.

Example 2.-1mage development The latent electrostatic image can bedeveloped on the electret by dusting with a suitable pigment powder in athermoplastic resinous base wherein the pigment powder is attracted tothe charged areas of the electret in amounts proportional to the densityof charge thereby to provide a corresponding density of color in thedeveloped image 36, as described in U.S. Patent No. 3,060,051, or thecopending application of Averbach, Ser. No. 97,162.

Example 3.-Preparat0n of copy In accordance with the practice of thisinvention, the preparation of copy from the developed latentelectrostatic image, without destruction of the latent electrostaticimage so that additional copies can be produced from the imagedelectret, is accomplished by arrangement of the electret with the tonedelectrostatic image in surface contact with a sheet of copy paper 38 andwith the assembly positioned between electrically conductive plates 40and 42 to which a potential can be applied. In this arrangement, theplates 40 and 42, when charged, function as a capacitor while theassembly of the electret 14 and copy sheet 38 functions therebetween asthe dielectric. in response to the application of a potential onto theplates 40 and 42, it will be found that when the sheets are removedfrorn between the plates and when the copy sheet 38 is stripped from theelectret 14, the toner will be retained on the copy sheet to form thedeveloped image 44 thereon, while the electret will still retain thelatent electrostatic image in sufcient intensity and in sufficientdetail to enable re-development of the latent electrostatic image byreeapplication of the pigment powder or toner.

The toner in the image developed on the copy sheet 3S can be set byconventional means, such as by heat, solvent, adhesive or the like, toproduce permanent copy. By the same token, the latent electrostaticimage 36 in the electret can be again toned by the developingcomposition to develop the image which can again be transferred toanother copy sheet for the production of an additional copy. It has beenfound that this can be repeated a number of times before the latentelectrostatic image becomes weakened or else spreads to the extent thatcopy of good quality can no longer be produced. When this occurs, thelatent electrostatic image can be wiped from the electret by exposure toradiation, such as light, infrared or ultra violet, and the electret canthereafter be recharged and exposed to form another latent electrostaticimage from which one or more copies can be produced in accordance withthe manner described.

' of the electret or to induce its own overall charge on the plate towipe out the image. Thus for imaging the plate in accordance with theprocess of the aforementioned article of Kallmann et al., wherein theelectret is exposed to a D-C field of 5 0-5 00 volts with simultaneousexposure,

' a potential of 2 kv. is sufficient. Thus, in general, it is desirableto make use of a potential for transfer which is greater than 50 voltsbut less than 5 kv. for an imaged electret developed in accordance withthe teachings of the aforementioned article and it is preferred to makeuse of a potential within the range of 50 volts to 3.5 kv.

As the plates 40 and d2, between which the copy sheet and electret aredisposed for image transfer, it is desirable to make use of a thin buthighly conductive material, such as sheets of copper, aluminum or steel,or use can be made of such materials as Nesa glass and the like. It ispreferred to dimension the plates to extend beyond the portions of theelectret and copy sheets from which transfer is to be effected. Bestresults are secured when the copy sheet and the adjacent plate aredisplaced together from the surface of the toned electret, but goodresults will be secured by removal of the plate prior to the removal ofthe copy sheet.

Example 4 When employing the process of selective depolarization fordevelopment of the latent electrostatic image on the phosphor layer, aD-C potential of 50-500 volts is applied, as in Example 1, across theentire layer with simultaneous radiation of the entire surface by lightto provide an overall polarization in charging the layer. The image isthereafter written into the layer by selective radiation in the absenceof an external eld to destroy the internal polarization in the exposedportions. This leaves the layer with polarization in the unexposedportions to provide the latent electrostatic image which can bedeveloped and transferred as in the previous Examples 3 and 4.

It will be apparent from the foregoing that we have provided a meanswhereby use can be made of a latent electrostatic image in an imagedelectret to produce multiple copies from a single exposure thereby tointroduce great flexibility in this new form of dry copy process.

It will be understood that changes may be made in the details ofconstruction, arrangement and operation, without departing from thespirit of the invention, especially as defined in the following claims.

We claim:

1. In an electrostatic copy process, the method of producing more thanone copy from an imaged electret comprising the steps of:

(a) positioning the electret layer between electrodes and passing a D-Cpotential between the electrodes, Vsimultaneously exposing the electretlayer to radiations over its entire surface internally to polarize theelectret layer, exposing the polarized electret layer to a light patternin the absence of the electrical field to eliminate the internalpolarization from the exposed areas, developing the latent electrostaticimage in the electret with a toner;

(b) positioning a copy sheet in surface Contact with the toned side ofthe electret; t

(c) positioning the copy sheet andV electret betwee electrodes;

(d) passing a potential between the electrodes whereby toner transfersfrom the imaged electret to the adjacent surface of the copy sheet toform an image thereon without destroying the latent electrostatic imagein the electret;

(e) separating the copy sheet and the electret from between theelectrodes; Y

(f) separating the copy sheet from the electret; and

(g) setting the toned image on the copy sheet.

2. The copy process as claimed in claim 1 in which the potential passedbetween the electrodes is greater than the potential used for imagingthe electret.

3. The copy process as claimed in claim 1in which the potential passedbetween the electrodes is more than 50 volts but less than 5 kv.

4. The copy process as claimed in claim 1 in which the copy paper andelectrode adjacent to the copy paper are removed together from thesurface of the electret.

5. The copy process as claimed in claim 1 which includes the step ofredeveloping the latent electrostatic image in the electret subsequentto separation from the copy sheet to retone the latent electrostaticimage and repeating steps (b) to (g).

6. In an electrostatic copy process, the method of producing more thanone copy from an imaged electret in the form of a phosphor layercomprising the steps of (a) positioning the electret between electrodesand passing a D-C potential between the electrodes, simultaneouslyexposing the electret layer to radiations in the form of a light patternto effect internal polarization in the exposed portions, developing thelatent polarized image in the electret with the toner;

(b) positioning a copy sheet in surface contact with the toned side ofthe electret;

(c) positioning the copy sheet and electret between electrodes;

(d) passing a potential between the electrodes whereby toner transfersfrom the imaged electret to the adjacent surfaces of the copy sheet toform an image thereon without destroying the latent electrostatic imagein the electret;

(e) separating the copy sheet and the electret from between theelectrodes;

(f) separating the copy sheet from the electret; and

(g) setting the toned image on the copy sheet.

7. The copy process as claimed in claim 6 in which the potential passedbetween the electrodes is greater than the potential used for imagingthe electret.

8. The copy process as claimed in claim 6 in which the potential passedbetween the electrodes is more than 50 volts but less than 5 kv.

9. The copy process as claimed in claim 6 in which the copy paper andelectrode adjacent to the copy paper References Cited UNITED STATESPATENTS 8/ 1956 Steinhilper 101--426 3/1961 Rose 96-1.8

OTHER REFERENCES IBM Tech. Disclosure Bnl-Schaffert-Multiple CopyPrinting Process, vol. 1, No. 4, December 1958.

NORMAN G. TORCHIN, Primary Examiner. R. E. MARTIN, Assistant Examiner.

